Faults in production machines such as, e.g. ring spinning machines, repeatedly give rise to periodic cross-sectional fluctuations in the test material, such as, e.g. in yarns. Front cylinders running out of true in ring spinning machines are particularly responsible for such cross-sectional fluctuations. These result in the known, disturbing moire' effects in the finished products. An eccentricity of a front cylinder of just, e.g. 0.1 mm, has a very disturbing effect. Although most front cylinders are sufficiently true-running, it is not uncommon to find so-called mavericks, i.e, front cylinders which give rise to considerable cross-sectional fluctuations in the yarn.
However it is very difficult, for example in ring spinning machines, to detect production stations which give rise to defects in the yarn or test material. It is in most cases hardly possible to visually detect any eccentricity. It would in principle be possible to carry out measurements with a dial gauge. However such measurements are so complicated that they are confined to just individual cases or research.
In practice only the finished yarns are subjected to quality control in the spinning mill. This has until now been carried out in the laboratory by means of random samples. In this case, however, it would be extremely valuable to detect the so-called mavericks, i.e. the inadequately running production stations. Yet this is only possible with full-scale control, not just with random samples. However a spinning mill has tens of thousands of production stations. Routine quality control directly at each production station is therefore absolutely unrealistic on account of the large number of production stations. There are no existing methods or devices which are able to meet the above requirement in any form, even just to a certain degree.